BRIDGEPORT — Metro-North called it a “tap,” but city officials said three of the railroad’s workers were injured Thursday afternoon when two trains collided on the tracks near Harbor Yard.

There was no immediate indication of just what went wrong, and it would likely be a while before full details emerged.

“We have inspectors on the way to the scene to assess the situation,” said Marc Willis, deputy director of public affairs for the Federal Railroad Administration. “Our investigations take time to complete.”

A Metro-North spokesman did confirm Thursday evening that the trains, which the railroad said were not carrying paying passengers, hit each other at about 1 p.m.

Two of the workers were described by Bridgeport city officials to be “walking wounded,” without any serious injuries, while the third sustained more serious, unspecified injuries, officials said. No updates on their conditions were available later.

“Both trains were going east,” said a Metro-North official who declined to speak for attribution, “One just tapped the other from behind.”

The collision drew an immediate response from local and railroad personnel. At least four ambulances, two ladder trucks, two fire engines, six police cars, several Metropolitan Transit Authority police personnel and State Police units responded to the scene.

“Collision would be a strong word,” Bridgeport Fire Chief Richard Thode said following the incident. “Both trains were going very, very slow and they bumped.”

Impact to the city, trains

Of the three injured workers, Thode said, two of them were taken away on stretchers.

The four tracks just south of the Bridgeport Metro-North station were shut down for about 30 minutes while first responders worked to the get all the train occupants safely off the tracks.

A Metro-North spokeswoman said one train was an equipment train and the other was a train without any passengers on it. She said both trains were traveling at low speeds.

Both were pulled by locomotives. One was an empty Waterbury branch Metro-North train and the other was a Metro-North service train. They collided between the Bridgeport train station and Main Street overpass.

With all the emergency vehicles on Ferry Access Road, those taking their cars on the Bridgeport-Port Jefferson Ferry were sent to the ferry entrance near the intersection of State and Water streets — usually only open to foot traffic.

Following Thursday’s collision, train service saw residual delays on the New Haven and Waterbury lines. Within a few hours, service was back on schedule.

Investigation under way

Jim Cameron, who covers transportation issues as a columnist for Hearst Connecticut Media, said he was sure the FRA would be thorough in its investigation, “but we may not get a report on this for months.”

Cameron said since a serious 2013 derailment of a Metro-North train in Fairfield, near the Bridgeport line, injured 75 people, the federal agency has had its eye on the railroad.

“I think anything that happens on Metro-North is going to be reported because of the FRA’s scrutiny of the railroad,” Cameron said.

After that derailment, he said, the FRA found that there was a pattern of on-time performance taking priority over safety — something that he said didn’t appear to be the case in Thursday’s collision.

“I’m not overly concerned (about Thursday’s incident) unless there proves to be a failure of the safety systems that are in place,” Cameron said.

Past incidents

In 2014, Metro-North worker Robert Luden was hit and killed by a train while working on a track that was supposed to be inactive.

Luden, 52, of East Haven, worked for the railroad for 27 years. He was hit by a commuter train had left the New Haven station, bound for New York City, at the West Haven train station while it was under construction.

An investigation was launched by MTA police, the Federal Railroad Administration, the National Transportation Safety Board and the New York State Department of Labor following Luden’s death.